I’ve over 900 hours played and when I download the game via Steam, I have nothing in my garage and none of the packs I purchased over the years. Basically it’s a fresh account.
I think you need to somehow link your accounts email to the steam login, i’m not sure how though and if you are having trouble doing it (or can’t find information on how to do it) you could send a support ticket:
Regards
Necronomica